Rear projection screens transmit an image from the back of the screen to the viewer on the opposite side of the screen. The image is affected by the amount of light transmitted by the screen or filter or throughput. Generally, screens and filters have been limited by their construction to the amount of light transmitted through the screen or filter. It is desirable to have constructions that provide increased light throughput and also provide improved contrast.
With increased definition of the projected image, the number of pixels has increased from the conventional number of several tens of thousands to a number exceeding one million pixels. As a result, there has been a demand for a finer structure of the lenses in the projection screen as well.
In concrete terms, there is a need to reduce the lens structure of current projection screens to a value of 0.36 mm or less in two of three dimensions.
Generally, rear projection screens have suffered from poor angularity. Angularity is the term used to describe the ability of a viewer to see a good image from the screen or filter at a range of angles other than those which are approximately orthogonal to the screen surface. As the viewer moves to the side of the screen or filter, or higher or lower than the screen or filter, the image brightness and/or quality is decreased. The angular brightness can be symmetrical or non-symmetrical and it is desirable to have screens and filters in which the image brightness and/or angular brightness can be tailored to best suit the intended viewing conditions.
It is typically advantageous to control the angular dependence of the screen's luminance by directing light to that region where the viewer is most likely to be positioned. For example, where the rear projection display is a data monitor, the viewer is typically positioned centrally relative to, and within approximately one to three feet from the display. The viewer's eyes may be positioned above a line normal to the center of the screen, but the viewer typically does not view the screen from a distance as much as one or two feet above the screen. Furthermore, for reasons of privacy or security, it may be desirable to reduce the luminance emerging from the screen at an angle or 30° or more relative to a normal to the screen. This reduces the possibility that someone positioned far away from the axis of the screen, and perhaps having no authority to view the contents of the screen, sees the information on the screen.
It is generally desirable to provide a rear projection screen that has high resolution, high contrast and a large gain.
U.S. Pat. No. 4,431,266 (Mori) relates to an optical refractor comprising of a plate of transparent material having a first and second surface. Segment lens elements of the same size are arranged on the first and second surface of the plate and formed integrally with the plate. The segment lens elements on the first surface are positioned in face-to-face relation with the segment lens elements arranged on the second surface.
U.S. Pat. No. 4,490,010 (Honda) relates to a rear projection screen consisting of an array of convex lenses on the front and rear sides of the screen. Projections or raised portions are provided which surround the front convex lenses and are extended forwardly thereof and light masking strips or layers are formed over the projections or raised portions.
U.S. Pat. No. 5,066,099 (Yoshida) relates to a rear projection screen image display device that comprises one or more sheet members through which light is sequentially transmitted from the side of a plane of incidence of the screen, the last sheet member comprising a transparent material as a base thereof, and a light diffusing layer provided on the side of a plane of emergence of the base. The light diffuser itself may be colored in order to obtain further enhanced contrast.
U.S. Pat. No. 5,870,224 (Saitoh) relates to lenticular sheet in which cylindrical lens parts including a radiation curable resin are formed on one side of a transparent support, and at least a light-diffusing layer and light-blocking stripes are formed on the flat surface located on the opposite side of said sheet. Cylindrical lens parts with a fine pitch of 0.3 mm or less can be obtained.
U.S. Pat. No. 5,933,276 (Magee) relates to a partially transparent, directional viewing sheet formed of plastic material with convex and concave lenses of elliptical cross-section formed on the front and back surfaces of the sheet.
U.S. Pat. Nos. 5,563,738 and 5,781,344, (Vance), relate to light transmitting and dispersing filters having low reflectance. The multi-layer light filters use the addition of optical layers to a basic refractive light filter to allow adjustment of gain, contrast and ambient light rejection of light filters.
U.S. Pat. No. 6,076,933 (DiLoreto et al.) describes light transmitting and dispersing filters similar to those described by Vance with the addition of a conformal layer of light transmissive material on the back surface of the transparent beads.